1. Field of the Invention
The present invention relates to safety barriers. More particularly, the present invention relates to safety barriers which utilize cable and to a method for erecting the barriers.
2. Technical Considerations and Prior Art
Over the past several decades, the number of automobiles and other vehicles on highways has increased drastically, while vehicle speeds have also increased. Accordingly, it has become necessary to erect safety barriers along highways to prevent vehicles out of control from leaving their designated lanes and perhaps crashing into other vehicles on the highways or structures positioned adjacent to the highways.
Originally, safety barriers were constructed by simply arranging rows of concrete posts adjacent to highway lanes. Then safety barriers were made by constructing continuous walls of concrete to a height of perhaps a couple of feet above the ground. Currently, it is general practice to make safety barriers of pressed metal strips and, in some instances, steel cables have also been used. These safety barriers, however, leave much to be desired because they are generally static and have low energy absorption. Consequently, when a vehicle strikes these types of barriers, the vehicle is often demolished and the passengers injured due to transmission of shock from the crumbling vehicle to the passengers. In addition, the vehicles often rebound back into the line of traffic, hitting other cars and causing additional accidents. Often, these barriers cause vehicles striking them to turn over, causing additional injury and damage.
In addition to damage to the vehicles and injury to passengers, the afore-described safety barriers are frequently damaged themselves upon impact. Consequently, these safety barriers must be frequently repaired, which is often a time-consuming and expensive procedure.
Steel cables are currently used as highway safety barriers because they generally have high rupture strength and are flexible, which facilitates installation and repair. However, steel cables have certain disadvantages when used as highway safety barriers because they are subject to moisture corrosion, chemical corrosion and electrical corrosion. This corrosion problem could, of course, be avoided by utilizing stainless steel, but the expense of stainless steel prohibits such use. In addition, steel cables have a lot of resistance to traction shock because relatively little energy per weight of material is needed to rupture the cable. This causes the cable to break upon being impacted by a vehicle and to whip around, causing additional hazards to other vehicles on the highway. Although the flexibility of steel cable makes it perhaps easier to install and handle than steel rails and the like, the high density of the cables which is manifest in a low kilometric rupture strength makes the placement of heavy cables suspended between spaced supports both difficult from an engineering standpoint and cumbersome. In order to avoid corrosion, periodic maintenance such as greasing, painting and tarring is necessary which, of course, is disagreeable, dirty and hazardous work. For these reasons, steel cables are not often used as safety barriers even though they might initially appear to have certain advantages over other types of safety barriers. Utilization of steel cables in safety barriers is exemplified by the British Patent No. 1,012,212 issued to H. M. Bender.
In order to overcome the difficulties encountered in utilizing steel cables as safety barriers, the prior art suggests utilizing a combination cable which has both steel strands and synthetic strands. Such a concept is exemplified by British Patent No. 1,272,588 issued to R. E. Campbell. In this patent, the strands composing the cable are made of helically wound filaments which may be either steel or alternately steel and synthetic materials.
Utilization of a rope or cable as a safety barrier wherein the rope or cable is manufactured from synthetic material such as nylon, rayon or the like is disclosed by U.S. Pat. No. 2,841,046 issued to L. A. Runton. In this particular patent, the barrier is not utilized for arresting motion of wayward highway vehicles, but is rather utilized to absorb shock from opening parachutes or as a harnass to capture runaway jet airplanes. The particular rope or cable disclosed in this U.S. patent utilizes 300,000 or more strands of crimped continuous filaments enclosed in a sheath. The cable disclosed in this U.S. patent, however, due to its structural complexity and expense, would not be suitable for extensive use as a highway safety barrier.